can't ping to my VMWare CentOs after seting host name

Linux and Unix-Like Red Hat
1

Im using CentOs 5.5 , i tried to change the host name to be for example my_server_1 , according to the web i changed the /etc/sysconf/network to look like this :

NETWORKING=yes
NETWORKING_IPV6=no
#HOSTNAME=localhost.localdomain
HOSTNAME=my_server_1

and changed the hosts file to look like this :.

127.0.0.1               localhost.localdomain localhost
192.118.5.72            my_server_1.com my_server_1
::1             localhost6.localdomain6 localhost6

in the apache server i changed the key of ServerName to be :

ServerName  www.my_server_1.com:8888

the 8888 port is open and working great if i use only ::8888 , in the Apache and to pinging
i restart the OS , and i can't ping to my_server_1 what else i need to do ?

2

hostnames cannot contain underscores.